Data communication between different stages of film use and processing (e.g. a camera user and dealer or photofinisher) has traditionally required separate written forms. This has not proven to be a very convenient or efficient method of relaying important information from one stage to another.
An innovation in data communication for motion picture film was introduced as described in the publication "DATAKODE Magnetic Control Surface" by Eastman Kodak Company 1983 (Publication No. V3-517). A thin layer of magnetic oxide was coated across the entire back surface of a roll of motion picture film to provide the capability to magnetically record digital data on the film without interfering with normal photographic use of the film. This permitted recording of different types of digital data at different stages of production of a motion picture which allowed for information exchange such as camera, lighting and filter data at the time of shooting to printer exposure control information in the laboratory to theater automation control signals during exhibition.
More recently, it has been proposed to employ a virtually transparent magnetic layer on still photography filmstrip to allow for magnetic recording of data in one or more longitudinal tracks associated with individual film image frames for information exchange purposes. An example of such a system is described in commonly assigned U.S. Pat. No. 4,965,627 issued Oct. 23, 1990. In order to provide quick access to particular data at any stage of film use, related data is preferably grouped and recorded in specific predetermined tracks. Camera data is recorded in several dedicated longitudinal tracks located along the filmstrip edges. The data is preferably recorded in pulse position encoded form in order to be independent of film transport velocity.
There has also been proposed, recently, camera systems that allow for removal of a film roll before all available film frames have been exposed, and later insertion in the same or different camera for exposure of the remaining film frames without double exposure of the previously exposed frames. This feature is generally referred to as "Mid-Roll Interrupt". While a number of arrangements have been proposed for implementing this feature, one that is generally accepted involves detecting the existence of magnetically recorded data adjacent exposed frames during loading of the film into the camera to position the film at the next available unexposed frame as indicated by the absence of recorded data. In less expensive MRI-equipped cameras it is necessary only to detect the existence of recorded data without decoding the detected data to implement the MRI function. In more sophisticated cameras, it may also be required that the data be decoded for transfer of operating control information to the camera controller while at the same time serving as an indicator of exposed frame positions.
For cost reasons it is desirable to have available integrated circuit chips that are capable of use in a multiplicity of camera designs, e.g. both the lower cost and more sophisticated cameras. Additionally, it is important to recognize that the magnetic layer employed as a virtually transparent layer on photographic film results in extremely small signal levels produced by the size constrained multi-turn inductive read heads that are usable in modern small camera designs. It is important that the MRI feature be able to discern proper signals from "background noise" in the camera system particularly since it is important that the MRI implementation be able to notify the camera system with a high degree of probability that a film frame has previously written magnetic data on it.